Tracking device



April 26, 1949.

s. D'ARLINGTON ET AL TRACKING DEVICE l Filed July 17, V194s 9o' PHA se .9H/F TER R6 C. A. LOI/ELL BV ATTORNEY Patented Apr. 26, 1949 UNITED STATES PATENT OFFICE TRACKING DEVICE Application `luly 17, 1943, Serial No. 495,131

4 (Jlaims. l

This invention relates to tracking devices and particularly to devices for tracking in slant range.

The object of the invention is a means for causing an indicator to track the slant range of an object moving at constant speed and constant height.

A feature of the invention is a means for deriving a motion proportional to the horizontal ground speed of the object.

Another feature of the invention is a means for controlling the tracking of the slant range by the derived value oi the ground speed.

Other features and advantages oi the invention will be apparent from the following description, and the drawing, which discloses a typical embodiment of the invention.

In many locating systems, such as anti-aircraft directors and computing sights for aerial bombing, the slant range or distance from a fixed point to a moving aircraft is continuously measured. In precision bombing, the aircraft must fly for an appreciable distance at constant speed and constant height. The slant range or distance may be measured from a xed position on the ground to the moving aircraft, as in anti-aircraft artillery operation, or from the moving aircraft to a position on the ground, as in aerial bombing.

Theslant range may be measured by an optical range nder, by two station ranging, or any opticaL'sonic, radio, or other method. In all such devices, the value of the slant range is manifested by some indicator. The object of the present invention is to control an indicator to follow the movement of the indicator on the range iinder. Purely for the purposes of description, and' not as any limitation on the scope of the invention, the present invention is shown operating in conjunction with a radio range iinding system of the type shown in British Patent 535,120 accepted March 28, 1941, Compagnie Generale de Telegraphie sans Fil. In this system, the slant range is indicated by a bright spot on the screen of a cathode ray oscilloscope, the bright spot being traversed laterally across the screen proportionately to the Slant range.

The range is indicated as a bright spot on the l screen I of the cathode ray oscilloscope. An indicator 2, which may be in the form of a thin pointer, is mounted on a nut 3 laterally traversed across kthe screen or" the oscilloscope by the threaded rod d iournaled in suitable bearings ii and rotated by the motor 5. A wiper l mounted uponyor driven by, the nut 2, but insulated therefrommoves along the potentiometer Winding .3.

A battery 9, or other suitable supply of voltage, is connected across the winding 8 of the potentiometer, the positive pole of the battery being grounded. A second battery I0, or other suitable supply of voltage, is connected across the Windings i'I and I2 of two other potentiometers, the negative pole of the battery I0 being grounded. The potentiometer windings 8, II and I2, are so designed that the voltages selected by the wipers 'I, I3 and I4 are respectively proportional to the square of the respective displacements of the Wipers. The potentiometer windings may conveniently have the Shape of long comparatively thin sheets of insulating material, closely and continuously wound with insulated wires. The sheets of insulating material are formed with one straight edge, along which the insulation of the wires is removed and on which the wiper is moved., the other edge being shaped to give the desired variation in voltage. If we let W(X) equal the width of the strip of insulating material at any given point X, R equal the resistance per unit length of the resistance wire, N equalfthe turns of the wire per unit length of the card, and RM equal the total resistance of the potentiometer winding, then the resistance per unit length-of the sheet of insulating material is equal to 2NRW(X) and the total resistance from one end of the card to the Wiper located at a displacement X,

1 dR(X) WX) '"2NR' 1X As the voltage is to vary in accordance with the square of the displacement of the wiper, in the present case The wiper I 3 is adjusted to a displacement proportional to the known height H of the aircraft.

The voltages selected by the wipers "I, I3 and it are supplied through the individual resistors I5, I6 and I'I to the input of a thermionic ampliiier i8, which may be in the form of a double triode. The thermionic amplier I8 is coupled to the thermionic amplifier I9 by a suitable interstage coupling network, which may be of the type disclosed in United States Patent 1,751,527,

,a March 25, 1930, H. Nyquist. The thermionic amplifier I9 is similarly coupled by a suitable-interstage coupling network to the thermionic ampliiier 2li.

The cathodes of the ampliers I8, i9 and 2li are heated by conventional means (not shown).

A battery 2 l, or other suitable source or supply, supplies anode current through the coupling resistor 22 to the anode of the amplifier Ztl. The winding of a relay 23, in series with a battery 2li, or other suitable source of voltage is connected across the output circuit of the amplifier 2li. The voltage of the battery 2li is selected so that in the absence of a signal applied to the control grid of the ampliiier i3, the positive voltage from the battery 2li exactly equals the positive potential oi the anode of the amplifier 2i), thus no current flows in the winding of the relay 23. The relay 23 is a polar relay normally biased to midposition, and capable oi making contact with contact Z5, or with contact 265, depending upon the polarity of the voltage applied to the winding of the relay 23.

A portion of the output of the ampliiier IQ is supplied to the potential divider formed by the resistors 2l and 28 in series. A portion of the potential drop in the resistor 28 is selected by the Wiper 29 and supplied to the control grid of the lower section of the double triode I8. The voltage from the Wiper 29 iorms a negative, or reverse, feedback to the input of the amplifier IB. A large value of negative feedback is used, and this large value of feedback has the effect of making the apparentl input impedance of the amplilier E8, as viewed from the input grid of a very low value, thus no interaction is produced between the voltages selected by the Wipers l, i3 and lll. The large value of negative feedback also makes the amplification for any input substantially independent of the amplifying properties of the vacuum tube, and dependent only upon the relative magnitudes of the resistances of the resistors 2l and 28, compared to the resistances of the resistors l5, It and Il. If the resistanoes of the resistors l5, I6 and Il are equal, then the voltages selected by the Wipers l, i3 and lll Will all be equally amplied.

A resistor 3Q, of comparatively high resistance, is connected between the cathode of the amplier i8 and ground, in order to couple the lower section of the double triode to the upper section. A battery Ill or other suitable source of supply, is connected in series with the resistor 3B and adjusted so that in the absence of an applied signal the cathode of the ampliiier i8 is at ground potential.

A capacitor 32, connected across the resistor 28, assists in producing rapid and accurate operation of the relay 2S. A battery 33 or other suitable supply of voltage, supplies a potential through the resistors 34 and 35 to the control grids of the lower section of the amplifier I8 and the amplier 20.

The voltage selected by the wiper i is proportional to S2, the square of the slant range; the voltage selected by the Wiper i3 is proportional to H2, the square of the height; and the voltage selected by the Wiper lil is proportional to R2, the square of the horizontal range. The height H, and the horizontal range R, are the two sides of a right triangle, of which the slant range S is the hypotenuse. Thus the voltages supplied to the input of the ampliiier E3 are proportional to H2-|-R2-S2, and if the wipers of the potentiometers are in the correct positions the sum of these voltages will equal zero. If the wipers of the potentiometers are not in the correct positions,

the sum of the applied voltages Will not be equal to zero, and a deviation voltage will be applied to the amplifier 2li, causing the relay 23 to Operate in a direction determined by the polarity of the deviation voltage.

Current is supplied from a suitable source 35 through the S30-degree phase shifting network 31 to one Winding of the motor 6, which may conveniently be a two-phase motor. Current can also be supplied from the source 36 and the transformer 38, through the contact of relay 23 when operated, to the other phase of the motor E. The phase of the current supplied by the transformer 33 to the Winding of the motor `i5 is determined by the contact 25 or 26 of the relay 23 which may be closed. Thus the operation oi the relay 23 will cause the motor 5 to operate in such a direction as to move the wiper l along the potentiometer winding until the deviation voltage is reduced to Zero, and the relay 23 is released.

Current is also supplied from the source 3% or any other convenient source of power, through the transformer il@ to the anode circuit of a gaseous disci urge, or trigger tube 1li. The winding oi a small direct current motor i2 is connected in series with the gaseous discharge tube (il, which acts as a single wave rectifier to supply pulsating unidirectional current to the motor 42. A battery 13, or other suitable source of voltage having an intermediate tap connected to one side of the windingr of motor l2 is connected across the winding of a potentiometer trl, the wiper of the potentiometer being connected to the control grid of the gaseous discharge tube fil. By adjusting the wiper or" the potentiometer Il@ the electrical angle with respect to the alternating anode voltage or Jfiring of the gaseous discharge tube di may be varied, thus adjusting the speed of the direct current motor l2 over a wide range. The resistor d5 and capacitor QG, connected in series across the motor d2, assists in securing a smooth variation in speed oi the motor d2.

The motor l2 drives one pinion of a differential gear il, which transmits this motion to the other pinion, driving the wiper id.

If the aircraft is moving at constant speed, the ground speed, or rate of change in the horizontal range R is constant, thus if the wiper of the potentiometer fifi is adjusted to the correct value so that the motor i2 drives the wiper lli at the correct value, the motor E Will be controlled by the deviation voltage, so as to drive the wiper 'l at the correct speed to follow the steady change in the slant range S. rThis smooth automatic tracking or the slant range will thus eliminate the usual erratic errors produced by a human observer attempting to iollovv the movement of a moving aircraft.

By operating the handwheel t9 geared to the crown gear of the diierential lll, the wiper I4 may be rapidly displaced, either to correct for minor errors in the setting of the slant range indicator, or to shift the slant range indicator from the indication for one target to the indication for a second target.

What is claimed is:

l. In a system including measuring means producing indications of the slant distance between two relatively moving objects, an indicator tracking said indications, a iirst source of voltage of one polarity, a u'st potentiometer having a winding linearly varying in resistance per unit length connected across said rst source and a wiper, a second source of voltage of opposite polarity, a

second potentiometer having a winding linearly varying in resistance per unit length connected across said second source and a wiper displaced proportionately to the difference in elevation between said objects, a third potentiometer having a winding linearly varying in resistance per unit length connected across said second source and a wiper, thermionic means having an input circuit connected to said wipers for adding the voltages selected by all said wipers, and an output circuit, motor means connected to said output circuit and controlled by the deviation of the sum oi said voltages .from zero to adjust said indicator and the wiper of said rst potentiometer, other motor means for adjusting the wiper of said third potentiometer, and means for adjusting the speed of said other motor means to cause said indicator to track said indications of slant distance.

2. In a system including measuring means producing indications of the slant distance between two relatively moving objects, an indicator tracking said indications, a rst source of voltage of one polarity, a rst potentiometer having a winding linearly varying in resistance per unit length connected across said source and a Wiper, a second source of voltage of opposite polarity, a second potentiometer having a winding linearly varying in resistance per unit length connected across said second source and a wiper displaced proportionately to the difference in elevation between said objects, a third potentiometer having a winding linearly varying in resistance per unit length connected across said second source and a wiper, thermionic means having an input circuit connected to said wipers for adding the voltages selected by all said wipers, and an output circuit, motor means connected to said output circuit and controlled by the deviation of the sum of said voltages from zero to adjust said indicator and the wiper of said nrst potentiometer, a differential gear including an adjustable frame and two pinions, having one pinion adjusting the wiper of said third potentiometer, other motor means driving the other pinion of said differential gear, manually operable means for adjusting the frame of said differential gear, and means for adjusting the speed of said other motor means.

3. In a system including means for producing indications of the slant distance between two relatively moving objects, an indicator tracking said indications, a iirst motor driving said indicator, a rst source of voltage of one polarity, first means connected to said source and driven by said first motor to produce a voltage varying in amplitude proportionally to the square of said slant distance, a second source of voltage oi the other polarity, second means connected to said second source and adjusted to produce a voltage proportional in amplitude to the square of the diierence in elevation between said objects, third means connected to said second Source and controlled to produce a voltage proportional in amplitude to the square of the horizontal distance between said objects, thermionic means having an input circuit connected to said iirst, second and third means to algebraically add said voltages and an output circuit connected to said iirst motor, to cause said rst motor to drive said indicator and said irst means to reduce the output voltage of said thermionic means to a minimum value, a second motor driving said third means, a source of power connected to said rst motor, and manually controllable means connecting said second motor to said source of power.

4. The combination in claim 3 in which said manually controllable means controls the speed of said second motor.

SIDNEY DARLINGTON. CLARENCE A. LOVELL.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 2,134,901 Wey Nov. 1, 1938 2,145,591 Fitzgerald Jan. 31, 1939 2,401,779 SWaItZell June 11, 1946 

